1. Field of the Invention
The present invention relates to a video signal recording apparatus and, more particularly, to a video signal recording apparatus for recording a digital still image signal and an analog video signal on the same recording medium.
2. Description of the Related Art
In recent years, a demand for high-density recording has been increasing in the field of magnetic recording. To meet the demand, there has been provided a video tape recorder (VTR) of the type which is capable of effecting magnetic recording of high density by transporting a magnetic tape at a reduced speed.
However, a VTR provided with a fixed head for recording an audio signal has the disadvantage that if an audio signal is recorded on a magnetic tape which is being transported at the reduced speed, no large relative speed is obtained between the head and the tape and a sound of degraded quality is reproduced. As a means for solving this problem, a method has been proposed in which the length of each track scanned by a rotary head is extended with respect to the track length used in a conventional art and an audio signal, which is compressed along its time axis, is sequentially recorded in the additional portion of each extended track.
Such a method will be described below with reference to a VTR of the rotary 2-head helical scan type. In the conventional art, a magnetic tape is wrapped around a rotary cylinder through an angle which is slightly greater than 180 degrees. However, in the above-described method, a magnetic tape is wrapped around a rotary cylinder through an angle which is slightly greater than (180+.theta.) degrees. When an audio signal is to be recorded, the audio signal is converted into a PCM audio signal, and after the PCM audio signal has been compressed along its time axis, the resultant PCM audio signal is recorded on the extra .theta.-degree portion of the magnetic tape wrapped around the rotary cylinder.
FIG. 1 is a schematic view showing a tape transporting system for use in the above-described VTR. FIG. 2 is a schematic view showing the loci of recording formed on the magnetic tape by the VTR shown in FIG. 1.
Referring to FIG. 1, a solid line 1 represents a magnetic tape, and heads 3 and 4 are mounted on a rotary cylinder 2. As shown in FIG. 2, a plurality of tracks are formed on the magnetic tape 1, and each of the tracks includes an analog video signal recording area 5 and a digital signal recording area 6 in which a PCM audio signal is recorded. The analog video signal recording area 5 is traced by the head 3 or 4 during the rotation of the rotary cylinder 2 through an angular extent of 180 degrees, while the digital video signal recording area 6 is traced by the head 3 or 4 during the rotation of the rotary cylinder 2 through an angular extent of .theta. degrees.
As an applied example of the above-described method of recording a digital signal in one area while recording a video signal in another area, a method is proposed in which a still image is recorded in the aforesaid one area as a digital signal. In the case of a still image, it is possible to record all information representative of the still image on a magnetic tape by scanning a plurality of PCM (digital) signal recording areas 6. According to this method, it is possible to realize still-image photography utilizing a photographic apparatus and a recording medium both of which are of types identical to those used for moving-image photography. In addition, it is possible to provide a high-quality still image whose quality is higher than that of a still image obtainable by repeatedly reproducing an analog video signal from the same track on a magnetic tape in a conventional VTR while keeping the magnetic tape in a temporarily stopped state.
It has also been proposed to provide a video camera-integrated type VTR in which the above-described recording apparatus is incorporated in a camera-integrated type VTR so that still-image photography can be performed together with moving-image photography.
However, the above-described video camera (or video camera-integrated type VTR) having a still-image photography function has a number of problems which will be described below. In this kind of video camera, for example, the following three modes are available: (1) a mode for recording only a moving image in a moving-image recording area (the analog video signal recording area 5 of FIG. 2); (2) a mode for recording a moving image in the moving-image recording area and, at the same time, recording a still image selectively extracted from the moving image in a still-image recording area (the digital signal recording area 6 of FIG. 2); and (3) a mode for recording only a still image in the still-image recording area.
When either of the modes (1) or (2) is active, a moving image is recorded at all times, and it is possible to effectively utilize the entire recording area on the magnetic tape. During reproduction, an operator can view a reproduced image on a TV monitor or the like without experiencing any substantial problem. In contrast, the mode (3) is designed to record only a still image, and if the operator views a reproduced image after performing recording based on the mode (3), the operator will feel that a reproduced image is extremely uncomfortable, because no moving image is recorded in the portion of the magnetic tape on which a still image has been recorded in the mode (3). Furthermore, the mode (3) is uneconomical since it consumes a large amount of magnetic tape. In addition, since a moving image is suddenly disturbed during reproduction, the operator may feel uncomfortable. Particularly when the magnetic tape is made to transport at a high speed, a portion devoid of a reproduced image appears on the TV monitor so frequently that the operator feels visually, extremely uncomfortable.
Part (i) of FIG. 3 shows the state of recording on a magnetic tape in which image signals of three kinds based on the above-described three modes are recorded. Parts (ii) and (iii) of FIG. 3 show timings associated with moving-image recording and those associated with still-image recording, respectively, and Part (iv) shows tape-travel control executed on the basis of the timings shown in Parts (ii) and (iii). Part (i) shows the state of recording which has been made on the magnetic tape in accordance with the timings shown in Parts (ii), (iii) and (iv). In Part (i), MV and SV represent a moving-image recording area and a still-image recording area, respectively.
Initially, when moving-image recording is started at a timing t1, tape travel is initiated, and a moving image is sequentially recorded in the analog signal recording areas MV of a plurality of tracks until the timing of the end of the moving-image photography. Thus, as shown in Part (i) of FIG. 3, a scene A including fields A1 to An is sequentially recorded by one field in each track as an analog signal between the timing t1 and a timing t2. If an instruction to extract a still image is inputted at a timing t3 between the timing ti and the timing t2, a field image in a field Ai at that timing is recorded as a still image in the digital still image recording areas SV of a plurality of tracks during a predetermined time duration (T0).
The tape travel is stopped at the timing t2. When an instruction to record only a still image is inputted at the next timing t4, the tape travel is restarted and continued until the predetermined time duration T0 passes after the timing t4. Thus, a still image B captured at the timing t4 is recorded in the still image recording areas SV of a plurality of tracks as shown in Part (i) of FIG. 3.
Then, a still image C captured at a timing t6 is similarly recorded until a timing t7 during only the predetermined time duration T0. When this recording is ended, the tape travel stops at the timing t7.
If moving-image recording is restarted at a timing t8, the tape travel is restarted and the moving-image recording is carried out, and operations similar to those executed in recording the scene A are carried out (if a still image D is to be extracted at a timing t10, similar operations are carried out).
Referring to the portion of the moving-image recording area MV that corresponds to the portion of the still-image recording area SV in which the still images B and C are recorded, no moving-image data is recorded in that portion of the moving-image recording area MV over a time duration of 2T0. Accordingly, if the magnetic tape is reproduced, the previously-described problems will take place.
In the case of a camera-integrated type VTR capable of recording a digitized high-quality still image in a PCM recording area of a VTR tape (or magnetic tape), it is common practice to dispose a release button for PCM still-image recording, such as a camera's release button, in addition to a recording button for ordinary recording of a moving image.
However, a scene which the operator desires to preserve as a PCM still image is not necessarily a scene which the operator has recorded by pressing the release button at his own will. There are also some cases where the operator unexpectedly encounters a rare scene and fails to preserve it as a PCM still image.
In addition, in the case of the reproduction of an image which has been recorded on a magnetic tape by a video camera-integrated type VTR having the above-described still-image photography function, since an image recorded in the moving-image recording areas of a plurality of tracks on the magnetic tape is merely continuously reproduced, it is impossible to determine at what point in time a picture was recorded as a still image.
To aid in making such a decision, a predetermined marker may be recorded concurrently with the recording of a moving image. However, even if the marker is displayed while a moving image is being continuously reproduced, it is substantially impossible to instantaneously grasp the contents of a recorded still image since the contents of the reproduced moving image consistently vary one after another during display.